1, 25-Dihydroxyvitamin D3(1,25(OH)2D3) is a hormonal metabolite of vitamin D which is postulated to act via the genome to modulate calcium transport in intestine and bone. Recent data indicate that 1,25(OH)2D3 may function at novel targets like pituitary, pancreas, and mammry gland. We propose to employ established cell lines to elucidate the biological function of 1,25(OH)2D3 in three types of target tissues: i) mineral homeostatic, ii) calcium transfer, and iii) peptide hormone secreting. An osteogenic sarcoma cell line (ROS 17/2.8) will be used to investigate the action of 1,25(OH)2D3 in osteoblast-like cells of bone. Studies will focus on characterizing the effects of cellular 1,25(OH)2D3 stimulation on the distribution of receptors between cytoplasmic and nuclear compartments, the chemical nature of the receptor's nuclear binding sites, and its influence on regulatory elements of transcription. These parameters will then be correlated with potential endpoint bioresponses such as alterations in calcium influx/efflux, de nova synthesis of proteins, and changes in marker proteins and enzymes like CaBP, collagen, and vitamin D-24-OHase. As an example of a calcium transfer cell, a human breast cancer line (MCF-7) will be probed for responsiveness to 1,25(OH)2D3 as expressed by modulation of 45Ca dynamics and de novo protein synthesis. These putative responses in MCF-7 will be related to receptor-nuclear interaction by utilizing selective deoxynucleoprotein modifiers in culture (i.e., butyrate, actinomycin D, etc.). A peptide hormone secreting cell line derived from rat pituitary tumor, GH3, will be explored for possible effects of 1,25(OH)2D3 on growth hormone and prolacatin secretion. An alternative endocrine cell which will be analyzed is an insulin-secreting pancreatic tumor line (RIN). This continuous cell culture approach to 1,25(OH)2D3 function represents a new tool in the delineation of the molecular and biological features of the vitamin D-calcium endocrine system. A clilnical application of these studies will be assay of 1,25(OH)2D3 receptors in human fibroblasts and monocytes (est. in patients with vitamin D-refractoriness). Finally, this research may reveal new relationships between vitamin D and diseases which affect bone integrity, such as diabetes, pituitary abnormalities, bone neoplasia and metastasizing breast cancer.